1. Field of the Invention
This invention pertains to apparatus for vacuum forming a vehicle tire, wheel or the like, from a mixture of polyurethane constituents.
2. Prior Art
The present invention is in an improved vacuum forming apparatus that is versatile in its capabilities for forming, in a single casting operation, items such as a tire, wheel or the like. The improved vacuum forming apparatus includes a mold having a cavity that is in the shape of an item to be cast, and which cavity can be formed to accommodate a core, such as a core of plies, belts and beads, for forming a tire in the apparatus. Or the core can be one formed from steel or an aluminum compound, for encapsulating a wheel, or the like, that can be supported in the mold by spacers, or the like. With either core to receive a polyurethane material flowing therearound. In practice, a polyurethane material, that is a compound formulated to produce a cured material having the desired characteristics of the item being cast, is pulled, under vacuum, into a mold cavity. After curing, the mold is opened, and a homogenous tire, wheel, or other item, including an item with a core encapsulated therein, is removed.
Recently, vacuum forming apparatus were developed by others from a recognition that venting air from a tire tread mold cavity early in a casting process could eliminate the necessity for venting the cavity through spaced holes in the mold that materials from the tread will flow into during casting and form projections or “tits”. The extensions or “tits” as project from the tire tread surface were either pulled off when the tire was removed from the mold, had to be cut off or wore off during tire use. To prevent this undesirable cosmetic anomaly it was recognized that air could be vented from the mold cavity just before tread casting, eliminating a necessity for providing flow passages or vents from the tire tread mold while still obtaining a smooth, un-pocketed or un-blemished, finished tread surface. Examples of such an introduction of a vacuum into a tire mold just prior to forming a tire tread are shown in U.S. Pat. Nos. 4,573,894 and 5,152,951. Specifically, U.S. Pat. No. 4,573,894 sets out a tire mold having a cavity that is for receiving and finally shaping the tire. The patent is defined by a surface that is for contacting the exterior of the tire during tire curing. The cavity is fluid connected to a single vacuum source for evacuating air from within the cavity during an early portion of a tire curing cycle to prevent air and any other fluid from becoming trapped between the tire and the surface that defines the cavity that will become the tire tread. Visual effects in the form of voids in the tire exterior are thus eliminated. Like the '894 patent, U.S. Pat. No. 5,152,951 also provides for the elimination of fluid from the mold cavity during an early portion of a tire curing cycle. The patent provides for fluid evacuation through a space between the surfaces of the mold parts that defines the mold parting line. Both patents provide a single vacuum source and its connection to the mold cavity for forming the tire side wall and tread surfaces.
Recently, the inventor of the present invention along with others developed “A Method and Apparatus for Vacuum Forming an Elastomeric Tire”, U.S. patent application Ser. No. 10/936,635, filed Sep. 04, 2004, and “A Method and Apparatus for Vacuum Forming a Wheel for a Urethane Material”, U.S. patent application Ser. No. 11/116,633, filed Apr. 29, 2005. These patent applications set out apparatus and methods for forming an elastomeric tire containing plies, belts and beads, and a wheel that may contain a metal core encapsulated by an elastomeric material, preferably a polyurethane material. Both applications involve an evacuation of air from the elastomeric mixture prior to its introduction into the mold cavity, and for pulling, under a vacuum, the air free mixture through the mold. Which air free flow of elastomeric material fills an area between inner and outer mold walls and for forming a tire, travels through the core of plies, belts and beads, producing a finished transport tire that is free of voids or pockets. With, for the other application, which elastomeric material, preferably a polyurethane, fills the mold cavity that has the wheel shape and may include a metal core.
The present invention is unique from the cited earlier vacuum forming apparatus in that it contains fewer seals and provides for a less restricted flow of a preferred urethane material through the mold cavity.